that was a tricky one, which had a relation with MOD maximum of 99m
With a 10/70 the MOD is deeper than 99 meters, but the output routine wouldn't print numbers bigger than 99 so it showed the 99. Internally, the correct MOD depth was written to the change depth setting - until you returned to surface mode, i.e. exited the menu: Upon returning to surface mode, all settings are checked against their allowed min/max values. Change depths were limited to 99 meters, the previously written value was > 99 and so it was reset to the air default of 56 meters... I've fixed the output routine and adopted the max limit, will be available in the next firmware version then.